The present invention relates generally to instruments used in ophthalmic surgery and, more particularly, to instruments used to mark the cornea prior to the implantation and alignment of an intraocular lens (IOL).
Replacement of a cataract with an artificial IOL is now a well-accepted surgical procedure. Typically, during such a procedure the diseased lens is removed from the capsular bag by phacoemulsification and a soft, plastic IOL is folded, inserted into the capsular bag and allowed to unfold to act as a replacement lens.
Early implantable IOLs did not afford any correction for corneal astigmatism and a patient suffering from such a condition would still have to wear glasses even after the cataract was removed and a new lens inserted in its place.
Alcon Industries has developed its AcrySof® tonic IOL which combines the flexibility of an implantable IOL with the astigmatic corrections available in typical glass or plastic eyeglass lenses. In order to use a toric IOL effectively, the lens must be rotated in the capsular bag to align the lens with a pre-calculated optimal axis, typically the steepest curvature of the cornea. To do so, a keratometer is used to measure the curve of the patient's cornea and to determine the steep axis of the cornea. When the toric IOL is implanted, a pair of reference marks on the toric IOL are aligned with the steep axis to provide the desired vision correction. As used herein, the term “keratometer” also refers to a corneal measuring device that includes means for placing marks on the cornea.
It is important to have an accurate measurement of the corneal curvature and equally important to find a method for identifying the steep axis during surgery so the IOL can be aligned properly.
The present invention relates to instruments which are used to mark the cornea of the patient to identify pre-phacoemulsification reference points to determine the orientation of the steep axis of the cornea so that after phacoemulsification the IOL can be rotated to align it properly with the steep axis.
Prior to phacoemulsification the patient's eye is examined with a keratometer and a toric IOL calculator is then used to determine the angle of the steepest, or “steep” axis along which the astigmatism is most pronounced and with which the lens needs to be aligned. The angle is then recorded so the IOL can be accurately aligned when inserted into the eye.
In preparation for surgery, the patient is seated in an upright position and a corneal marker is used to mark the 3-, 6- and 9 o'clock positions on the cornea, with the 3- and 9 o'clock positions corresponding to the corners of the eye and the 6 o'clock position corresponding to the bottom of the eye. These will be the reference points for later marking of the steep axis.
The corneal marker includes a series of tabs formed on the front surface of a circular ring, placed at 90° intervals. The rear of the ring includes a number of marking tabs intended to come into contact with the cornea. After the marking tabs are coated with dye, one marking tab is aligned with the limbus of the eye and the instrument is then pressed against the cornea to leave marks corresponding to the 3-, 6- and 9 o'clock positions.
A second corneal marker, made specifically for marking the steep axis has a pair of axis marking tabs on the rear and a scale on the front, marked in degrees. Some corneal markers may also include a rotating ring, commonly mounted within a fixed ring, with the fixed ring used to mark the reference points and a rotating ring used to mark the steep axis. The rotating ring has a pair of axis marking tabs formed on its rear surface.
When the patient is ready for surgery, one of the corneal markers described above is used to mark the steep axis. If the second corneal marker has a fixed set of tabs, the scale on the front of the marker is read to correspond with the steep axis by aligning the axis reading with the reference points already present on the cornea. If a corneal marker with a rotating ring is used, the marker is aligned with the reference points and the ring is rotated until the steep axis setting is reached and the marker is allowed to come into contact with the cornea to press the axis tabs, aligned with the angle marking on the marker, against the cornea. The axis tabs make a pair of marks on the cornea, and it is this second set of reference marks that identifies the axis with which the IOL is aligned when it is inserted so that the stigmatic correction of the IOL is maximized.
The corneal marker will work more accurately to make the reference marks if it is held in a horizontal position when the patient is sitting up. To position the marker, the user hold it to align the handle in a generally horizontal orientation. The marker will work most accurately if it is held in a horizontal position when the patient's eyes are also aligned horizontally, as in when the patient is sitting up. To position the marker, the user holds it in as horizontal an orientation as possible, aligns the marker with the patient's eye and then presses it against the eye so that the dye-coated axis tabs make the desired reference marks on the cornea. It is important for the corneal marker to be held as nearly level as possible during the marking process.
Examples of markers and tilt detectors are found in the prior art.
U.S. Pat. No. 6,217,596 (Farah) teaches and describes a corneal surface and pupillary cardinal axes marker having an inclinometer mounted on the frame.
U.S. Patent Application Publication 2008/0228210 (Davis) describes prior art markers having level gauges or plumb bobs to indicate when the marker handle is being held in the horizontal position.
U.S. Pat. No. 4,739,761 teaches and describes a cornea marker that employs a rotating marker wheel to allow the cornea to be marked at selected locations.
It is an object of the present invention to provide instruments useful for marking the cornea for the insertion and alignment of a multifocal IOL while allowing the surgeon to double check the location of the corneal steep axis prior to insertion of the lens.
It is a further object of the present invention to provide a convenient and accurate way in which to assure that the corneal marker and the patient's eye are properly aligned to make an accurate measurement.
While the following describes a preferred embodiment or embodiments of the present invention, it is to be understood that this description is made by way of example only and is not intended to limit the scope of the present invention. It is expected that alterations and further modifications, as well as other and further applications of the principles of the present invention will occur to others skilled in the art to which the invention relates and, while differing from the foregoing, remain within the spirit and scope of the invention as herein described and claimed. Where means-plus-function clauses are used in the claims such language is intended to cover the structures described herein as performing the recited functions and not only structural equivalents but equivalent structures as well. For the purposes of the present disclosure, two structures that perform the same function within an environment described above may be equivalent structures.